BERLIN – Tunisian suspect Anis Amri’s fingerprints have been found in the cab of the truck that plowed into a Christmas market in Berlin, strengthening the case linking him to the deadly attack, Germany’s top security official said Thursday.

Authorities across Europe were scrambling to find the 24-year-old suspect, a day after Germany issued a wanted notice for him and warned that he may be “violent and armed.”

In Berlin, the Christmas market that was ripped apart by the truck reopened — with increased security measures — in a signal of the city’s resilience.

German authorities have offered a reward of up to 100,000 euros ($104,000) for information leading to Amri’s arrest. Twelve people were killed and 48 injured in Monday evening’s rampage, which was claimed by the Islamic State group.

“We can tell you today that there are additional indications that this suspect is with high probability really the perpetrator,” Interior Minister Thomas de Maizière said after visiting the Federal Criminal Police Office along with Chancellor Angela Merkel.

“Fingerprints were found in the cab, and there are other, additional indications that suggest this,” he told reporters. “It is all the more important that the search is successful as soon as possible.”

In Tunisia, one of Amri’s brothers spoke to press to urge him to surrender to authorities.

“I ask him to turn himself in to the police. If it is proved that he is involved, we dissociate ourselves from it,” brother Abdelkader Amri told news agencies.

He said Amri may have been radicalized in prison in Italy, where he went after leaving Tunisia in the wake of the 2011 Arab Spring uprisings.

Amri’s mother said he had shown no signs of radicalization and questioned whether he was really the attacker. Speaking Thursday in the central Tunisian town of Oueslatia, Nour El Houda Hassani said poverty drove Amri to steal and to travel illegally to Europe.

She said Amri spent time in an Italian prison and in Switzerland before reaching Germany.

“I want the truth to be revealed about my son,” she said. “If he is the perpetrator of the attack, let him assume his responsibilities and I’ll renounce him before God. If he didn’t do anything, I want my son’s rights to be restored.”

Tunisian police who interrogated the family on Wednesday took away her telephone and were studying her communications with her son, she said.

German officials put out an arrest warrant for Amri, who according to authorities has used at least six different names and three different nationalities, after finding a document belonging to him in the cab of the market attack truck.

German authorities had deemed Amri, who arrived in the country last year, a potential threat long before the attack this week — and even kept him under covert surveillance for six months this year before halting the operation.

They had been trying to deport him after his asylum application was rejected in July but were unable to do so because he lacked valid identity papers and Tunisia initially denied that he was a citizen.

At the market outside Berlin’s Kaiser Wilhelm Memorial Church, police placed concrete blocks at the roadside Thursday to provide extra security as it reopened. In a solemn tribute to the victims, organizers decided to do without party music and bright lighting and Berliners and visitors laid candles and flowers at the site.

An Israeli woman, Dalia Elyakim, and 31-year-old Fabrizia Di Lorenzo of Italy were among the 12 killed in the market attack, their countries said. Di Lorenzo had lived and worked in Berlin for several years.

Two U.S. citizens were among the wounded, State Department spokesman John Kirby said.